Re: Problem with TIFF alpha channel
Re: Problem with TIFF alpha channel
- Subject: Re: Problem with TIFF alpha channel
- From: Chris Rudolph <email@hidden>
- Date: Tue, 9 Oct 2001 06:36:58 -0700
Hi Jeff,
How are you drawing the image? It looks like you need to use
'NSCompositeSourceOver' instead of 'NSCompositeCopy'. Check out the
NSImage method - 'compositeToPoint:operation:'
Cheers,
Chris.
--
Chris Rudolph, AppleWorks Engineering
Apple Computer, Inc.
email@hidden
On Monday, October 8, 2001, at 08:36 PM, Jeff Disher wrote:
Hello,
I am working on a program that reads in a 24-bit RGB
TIFF image from a file and adds an alpha channel to
make it into a 32-bit RGBA TIFF image which it then
displays on the screen.
So far, whenever I am adding the alpha channel to 100%
opacity (255 unsigned integer) the image displays
perfectly opaque and with the proper RGB data
expressed just as if it were a 24-bit RGB image.
However, if the alpha channel of any pixel is set less
than 100% the pixel appears as if it were black (but
the alpha value seems to be properly expressed). I
tried logging one of the pixels and its values are
what they are supposed to be. I also put the image in
the dock and it did properly act semi-transparent. I
also am confused by the way that an outline appears
around where the image should be.
Can anyone shed some light on this for me because I am
completely confused by this behavior?
Thanks,
Jeff.
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